This invention relates to controlling micro-electro-mechanical cavities.
As shown in FIG. 1, a micro-electro-mechanical structure (MEMS) 10 can be formed to have two walls 12, 14 connected mechanically 16 to define a cavity 18. The walls of the cavity can be movable relative to one another to control, for example, interferometric optical properties of the cavity. An electrode 20 can be formed on one of the walls so that, when a sufficient voltage VA (see FIG. 2) from a voltage source 24 is applied between the electrode and the opposite wall 12, the activation threshold of the cavity is exceeded and the wall 12 is drawn close to the wall 14 by electrostatic force 26. Because of a hysteresis effect, the wall 12 will then remain close to wall 14 even if the voltage falls below VA. Only when the voltage falls below a lower value, VB, will the wall 12 return to its original position.
In general, in one aspect, the invention features apparatus that includes a cavity having a cavity dimension, the cavity being configured so that the cavity dimension changes in response to electrostatic forces applied to the cavity, and at least two electrical structures configured to apply electrostatic forces in the vicinity of the cavity, the electrical structures being independently controllable.
Implementations of the invention may include the following features. The cavity dimension is determined by a distance between two walls, and the cavity dimension determines optical properties of the cavity. The optical properties include interference or reflectance. The two electrical structures comprise electrodes. The electrical structures lie on a wall of the cavity. The electrical structures lie side by side on the wall of the cavity. The cavity comprises an interference modulator and the cavity dimension determines an optical state of the modulator. Changes in the cavity dimension that occur in response to the electrostatics forces are characterized by hysteresis. There is also a second cavity adjacent to the cavity. The cavity and the second cavity share a common wall.
There are also stops within the cavity, the stops defining an intermediate cavity dimension between a minimum cavity dimension and a maximum cavity dimension the stops define channels between them portions of a wall of the cavity lie in response to electrostatic forces. One of the electrical structures comprises electrodes embedded within the stops. The stops lie on a movable wall of the cavity. Apertures in a second wall of the cavity are configured to receive the stops. There are also additional cavities having cavity dimensions, each of the cavities being configured so that its cavity dimension changes in response to electrostatic forces applied to the cavity. There are additional electrical structures configured to apply electrostatic forces in the vicinities of the cavities, each of the additional cavities being associated with at least two of the additional electrical structures. The electrical structures with which each of the cavities is associated are independently controllable. At least some of the electrical structures associated with at least some of the respective cavities are coupled together.
The cavities are organized in groups by coupling together of selected electrical structures. The coupling comprises bus conductors. The coupling comprises bus elements fabricated on multiple levels of the apparatus.
In general, in another aspect, the invention features apparatus that includes an array of interferometric modulators, actuation electrodes associated with the respective interferometric modulators, and a pattern of conductors connecting the actuation electrodes in groups.
Implementations of the invention may include the following features. The groups comprise rows or columns of the actuation electrodes. The groups comprise pixels of a display. Each of the interferometric modulators is associated with more than one of the electrodes. The pattern of conductors connects different ones of the electrodes associated with each of the interferometric modulators in a configuration that enables them to be energized independently. The electrodes are arranged on walls of cavities of the interferometric modulators.
In general, in another aspect, the invention features a method that includes energizing one electrical structure to apply an electrostatic force in the vicinity of a cavity, and independently energizing another electrical structure to apply an electrostatic force in the vicinity of a cavity.
Implementations of the invention may include the following features. The one structure is energized to move an element of the cavity to a first position, and the other electrical structure is energized to maintain the element in the first position. The one structure is de-energized while the other structure remains energized. The energizing of the one electrical structure and the other electrical structure is controlled to effect more than two optical states of the cavity. One electrical structure is energized to apply an electrostatic force in the vicinity of each of multiple other cavities, and another electrical structure is independently energized to apply an electrostatic force in the vicinity of each of the multiple other cavities. The energizing of the electrical structures is controlled to independently control the optical states of groups of one or more of the cavities.